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Mar11-12, 12:49 AM
P: 431
"It is important to realise that in physics today, we have no knowledge of what energy is.We do not have a picture that energy comes in little blobs of a definite amount.Is is not that way.However, there are formulas for calculating some numerical quantity, and when we add it all together it gives "28"-always the same number.It is an abstract thing in that it does not tell us the mechanisms or reasons for the various formulas."
(Reference:Feynman Lectures,Vol.I,Conservation of Energy)

If energy is only a number,why should it be difficult to see that work and heat(with their differences) are mere mathematical expressions with no mechanisms or reasons?(after all the first law says that energy moves about as work and heat only so the three are equivalent in this respect of being abstract)